A circuit interrupter is an electrical component that can break an electrical circuit, interrupting the current. A basic example of a circuit interrupter is a switch, which generally consists of two electrical contacts in one of two states; either closed meaning the contacts are touching and electricity can flow between them, or open, meaning the contacts are separated. A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch.
A second example of a circuit interrupter is a circuit breaker. A circuit breaker is used in an electrical panel that monitors and controls the amount of amperes (amps) being sent through the electrical wiring. A circuit breaker is designed to protect an electrical circuit from damage caused by an overload or a short circuit. If a power surge occurs in the electrical wiring, the breaker will trip. This will cause a breaker that was in the “on” position to flip to the “off” position and shut down the electrical power leading from that breaker. When a circuit breaker is tripped, it may prevent a fire from starting on an overloaded circuit; it can also prevent the destruction of the device that is drawing the electricity.
A standard circuit breaker has a line and a load. Generally, the line is the incoming electricity, most often from a power company. This can sometimes be referred to as the input into the circuit breaker. The load, sometimes referred to as the output, feeds out of the circuit breaker and connects to the electrical components being fed from the circuit breaker. There may be an individual component connected directly to a circuit breaker, for example only an air conditioner, or a circuit breaker may be connected to multiple components through a power wire which terminates at electrical outlets.
A circuit breaker can be used as a replacement for a fuse. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Fuses perform much the same duty as circuit breakers, however, circuit breakers are safer to use than fuses and easier to fix. If a fuse blows, oftentimes a person will not know which fuse controls which specific power areas. The person will have to examine the fuses to determine which fuse appears to be burned or spent. The fuse will then have to be removed from the fuse box and a new fuse will have to be installed.
Circuit breakers are much easier to fix than fuses. When the power to an area shuts down, the person can look in the electrical panel and see which breaker has tripped to the “off” position. The breaker can then be flipped to the “on” position and power will resume again. In general, a circuit breaker has two contacts located inside of a housing. The first contact is stationary, and may be connected to either the line or the load. The second contact is movable with respect to the first contact, such that when the circuit breaker is in the “off”, or tripped position, a gap exists between the first and second contact.
To trip, or break, a circuit, a solenoid with an overcurrent sensor may be used. When the overcurrent sensor senses a specific current level, or a percentage above the rated current, the solenoid may be actuated to mechanically move an arm tripping the circuit breaker from the closed to the open position.
There have been many proposed devices to mechanically trip a circuit breaker. U.S. Pat. No. 3,863,042 to Nicol discloses a circuit breaker having a handle stop for restraining the handle in a tripped or central position after the circuit breaker has been electrically tripped. The circuit breaker has a movable arm controlled by a toggle mechanism having its knee displaced by the arm of an armature of a coil. The disadvantage of this device is that it is only capable of immediately tripping the circuit breaker at a single current level. This is disadvantageous as the circuit breaker will accidentally trip on the detection of a low current spike, such as the starting of a motor. This renders the circuit breaker almost useless as the circuit breaker will be constantly tripping when the circuit breaker does not need to be tripped.
U.S. Pat. No. 5,089,797 to Grunert et al. proposes a circuit breaker with a single electromagnetically actuated plunger that may be actuated at two levels of excessive current or voltage defined by two air gaps, one at a lower level for triggering a toggle mechanism, the other at a higher level for directly actuating a movable arm through a kicker arm. The introduction of two current level allows the circuit breaker to prime the mechanism that trips the circuit breaker, and then trip the circuit breaker once the current reaches a certain level. As with Nicol above, a disadvantage of this circuit breaker is that it uses a single overcurrent coil to trip the circuit breaker and immediately trips after the detection of the second current level.
To prevent the circuit breaker from accidentally tripping, the tripping mechanism would have to be set to a high level, so that a small current spike would not result in the tripping of the circuit breaker. This, however, would not trip the circuit breaker in the event of a small current spike for an extended period of time, which can damage equipment connected to the circuit breaker.
Instead of setting the tripping mechanism at a high current level, many circuit breakers introduce a delay in the tripping mechanism so that the circuit breaker only trips after the detection of a current spike for a specific period of time. This prevents the circuit breaker from immediately tripping, thus preventing many situations where the circuit breaker would be accidentally tripped upon the detection of a low current spike, but would also protect the equipment from a low current spike that lasts for an extended period of time. The introduction of a delay, however, introduces a problem that can be very dangerous and can severely damage equipment. The introduction of a delay prevents the circuit breaker from immediately tripping when a high current spike, or a short, occurs. For example, if a person accidentally comes into contact with a live wire or live outlet, a large current spike may occur. Any delay in the tripping of the circuit breaker corresponds to an increase in the amount of time the person is in contact with the live wire or outlet. This can lead to severe injury, or even death. A short may also occur if there is a problem with the equipment connected to the circuit breaker, if the circuit breaker waits for a specific period of time to pass before tripping, the equipment connected to the circuit breaker may be severely damaged.
What is desired, therefore, is a circuit interrupter that can automatically trip the circuit at differing voltage or current levels and based on different durations of the voltage or current levels.